Hydrogen cyanide (HCN), (AC), also known as hydrocyanic acid or prussic acid, is a colorless to water-white or pale-blue liquid at temperatures below 80ºF. It has an odor of peach kernels or bitter almonds at 1-5 ppm. HCN may not have a detectable odor in lethal concentrations. The acute toxicity of hydrogen cyanide is high. There is rarely a reported chronic exposure to HCN because you either get better quickly from an exposure or you die. It is toxic by inhalation, skin, absorption, and ingestion, with a TLV of 10 ppm in air. The LD50 through ingestion is 10 mg/kg of body weight. Skin absorption LD50 is estimated to be 1500 mg/kg of body weight. Inhalation of HCN has an LC50 of 63 ppm for 40 min. OHSA has established a PEL of 10 ppm (11 mg/m³) for skin contact. TLV-TWA values are listed by ACGIH at 10 ppm (11 mg/m³) for skin absorption. Inhalation of 18-36 ppm over a period of several hours can produce weakness, headache, confusion, nausea, and vomiting. Inhalation of 270 ppm can cause immediate death, and 100-200 ppm over a period of 30-60 min can also be fatal. Absorption of 50 mg though the skin can be fatal. Ingestion of 50-100 mg of HCN can also be fatal.